A zero-turn mower is basically a riding lawn mower with a turning radius that is effectively zero inches. Such mowers can reduce the amount of time required to mow yards and other areas because they can cut closely around trees, fences, and other obstacles and therefore reduce or even eliminate the need for trimming. Another advantage of these mowers is that they pivot through 180 degrees without leaving a circle of uncut grass.
Different brands and models achieve a zero-turn radius in different ways, but hydraulic speed control of the drive wheels is the most common method. A typical zero-turn mower has each of its rear wheels connected to a separate hydrostatic transmission—a device that creates wheel rotation using pressurized fluid. Rotational force from an engine turns a pump that pressurizes transmission fluid. A steering/speed lever, joystick or other user control device may be moved to control the flow of fluid through each transmission and thus control the rotational speed or the forward/reverse direction of each drive wheel. If one drive wheel turns more rapidly than the other, the mower moves along a curved path. If both wheels turn at the same speed, the mower follows a straight path. If one wheel stops and the other turns, or if the wheels turn in opposite directions, the mower pivots or rotates.